The present invention relates to a soil improver (soil auxiliary substance) according to the preamble of claim 1 and also to the use thereof, in particular for improving soil quality, more particularly for increasing the water uptake capacity and/or water storage capacity of soils and/or for the loosening (e.g., aeration) of soils (e.g., in agriculture, in viticulture, horticulture, and landscaping, for sports, golf, gardening, lawn, and riding areas, for green roofing, for land consolidation, in particular on slopes, for combating desertification in arid regions, for plant growth promotion and regulation, or the like).
The prior art has disclosed numerous soil improvers. Oftentimes, however, they do not possess the desired efficiency, particularly not in relation to a promotional effect on vegetative growth. Furthermore, sufficient biocompatibility is not always ensured.
Thus DE 295 16 675 U1 describes a water storage soil auxiliary which comprises a hydrogel, alginate, and, if desired, clay. The material described therein does not contain sufficient amounts of plant nutrients. Nor is any delayed, long-term provision of plant nutrients possible. Moreover, hydrogels do not always have a sufficient water uptake capacity and water storage capacity, and, furthermore, in larger amounts they result in deficient aeration of the soil, producing the potential for the vegetation in question to suffer root rot.
Also given consideration in the prior art, furthermore, for the preparation of soil improvers have been materials known as superabsorbent polymer (SAP) materials. These superabsorbent polymers (SAP) have to date been used, on account of their high swelling properties and their water uptake capacity, with preference in the hygiene industry, as for example in diapers, sanitary towels, etc.
DE 101 30 427 A1 and its correspondent WO 03/000621 A1, and also DE 10 2005 021 221 A1 and its correspondent WO 2006/119828 A1, each describe porous, water-swellable polymers having a sponge structure and superabsorbent properties, in particular on the basis of polyacrylic acid, together with inorganic and organic ballast substances and adjuvants, and are said to be suitable as soil improvers. The organic polymers are based in particular on homopolymers or copolymers of acrylic acid with free carboxylic acid functions, the materials described therein being said to have water storage properties and consequently to find use inter alia as soil improvers. However, since the compositions described therein possess free carboxyl groups, their alkali susceptibility is relatively high, and this leads to reduced swellability and water uptake. Moreover, the material described therein is not in all cases sufficiently biocompatible and bioavailable, and in particular is not sufficiently rapidly degradable. Furthermore, on long-term use in soils, the material described therein has a proclivity to unwanted gelling, which is a hindrance in relation to plant growth, and in particular may damage root formation. Where additives are added, especially plant nutrients, there is no long-term effect, in particular no delayed release, since these substances are only separately added to the mixture described therein, but not effectively bonded thereto. In addition, the swelling behavior is not reversible under all conditions, and so stored water cannot be readily delivered from the material described therein to the plants again. Finally, the production methods described therein result in a relatively high residual monomer content in the end product, which is detrimental in relation to vegetative growth in the context of a soil improver utility.